El Niño (Spanish name for the male child),
initially referred to a weak, warm current appearing annually around
Christmas time along the coast of Ecuador and Peru and lasting only a few weeks
to a month or more.
Every three to seven years, an El Niño event may last for many
months, having significant economic
and atmospheric consequences
worldwide. During the past
forty years, ten of these major El Niño events have been recorded, the
worst of which occurred in 1997-1998.
Previous to this, the El Niño event
in 1982-1983 was the strongest. Some of the El Niño events
have persisted more than one year.

In the tropical Pacific, trade winds generally
drive the surface waters westward. The surface water becomes progressively
warmer going westward because of its longer exposure to solar heating.
El Niño is observed
when the easterly trade winds weaken, allowing
warmer waters of the western Pacific to migrate eastward and eventually reach
the South American Coast (shown in orange).
The cool nutrient-rich sea water normally found along the coast of
Peru is replaced by warmer water depleted of nutrients, resulting in a
dramatic
reduction in marine fish and plant life.